Apparatus for desolventizing solvent extracted milled rice and rice bran

ABSTRACT

A method and apparatus of desolventizing previously solvent extracted milled rice and, in certain embodiments of the invention, desolventizing of the bran removed from the rice. The method and apparatus contemplates using a desolventizing gaseous medium comprising inert gas as the major component thereof wherein the gaseous medium is contacted with the rice when at a temperature in the range from about 100* F. to about 150* F., whereby the solvent is vaporized from the rice at a relatively low temperature, thereby preserving the quality of the rice. The gaseous medium with the vaporized solvent entrained therein is subsequently condensed to remove the solvent therefrom and the medium is subsequently heated and recycled.

United States Patent 11 1 m1 3,714,719 Wayne Feb. 6, 1973 [54] APPARATUSFOR DESOLVENTIZING 2,571,143 10 1951 Leslie ..34 37 x SOLVENT EXTRACTEDMILLED RICE 2,618,560 1 l/1952 Leslie D C BRAN 2,81 1,539 10/1957Komofsky ..260/412.4

[76] Inventor: Truman B. Wayne, c/o Truman B. Primary Examiner xennethSprague Wayne & Assc" Box Assistant Examiner-James C. Yeung- HoustonAttorney-Delmar L. Sroufe et al.

[22] Filed: Feb. 1, 1971 [21] Appl. No.2 111,632

Related US. Application Data [57] ABSTRACT A method and apparatus ofdesolventizing previously solvent extracted milled rice and, in certainembodiments of the invention, desolventizing of the bran removed fromthe rice. The method and apparatus contemplates using a desolventizinggaseous medium comprising inert gas as the major component thereofwherein the gaseous medium is contacted with the rice when at atemperature in the range fromabout 100 F. to about 150 F., whereby thesolvent is vaporized from the rice at a relatively low temperature,thereby preserving the quality of the rice. Thegaseous medium with thevaporized solvent entrained therein is subsequently condensed to remove'the solvent therefrom and the medium is subsequently heated andrecycled.

4 Claims, 7 Drawing Figures PATENTEUFEB 6 I973 3,714 719 SHEET 2 BF 5APPARATUS FOR DESOLVENTIZING SOLVENT EXTRACTED MILLED RICE AND RICE BRANThis application is a division of application Ser. No. 695,632, filedJan. 4, 1968 which was a continuationin-part of copending applicationSer. No. 529,81 1 filed Feb. 21, 1966, by the same inventor.

This invention relates to a method and apparatus for desolventizingpreviously solvent extracted milled rice. More particularly, it relatesto a method of desolventizing solvent extracted milled rice with agaseous medium comprising inert gas as the major component thereof,wherein the gaseous medium is contacted with the rice at a relativelylow temperature andon the order of from about 100 F. to about 150 F.,whereby the quality of the rice is preserved during the desolventizingthereof.

There has recently come into use various apparatus and methods formilling and solvent extracting brown rice. Examples of such apparatusand methods are taught in the following U.S. Pat., for example: No.3,165,131,; No. 3,217,769; No. 3,261,690 and No. 3,330,666.

In the milling of rice, it is desirable to maintain as many whole milledkernels as possible with the smallest amount of checking or breaking aspossible. However, rice kernels, particularly milled rice, are verysensitive to changes in not only temperature, but water and sol-' ventcontent. During the process of removing the solvent from solventextracted milled rice, unless great care -is exercised, the rice kernelshave a great tendency to check or crack or break and in some instances,to assume an undesirable rather chalky white appearance.

Many apparatus and methods have been developed for the purpose ofdesolventizing various solvent extracted particles. Patents which arerepresentative of .the prior art include the following U.S. Pat.: No.

2,571,143; No. 2,618,560; No. 2,691,830 and No. 2,811,539.

However, it has been found that none of the prior art apparatus andmethods are completely successful with respect to the desolventizationof solvent extracted milled rice for various reasons, includingexcessive breakage of kernels by the violet agitation of the particles,excessive heat and the like.

It is therefore an object of this invention to provide an improvedmethod and apparatus for desolventizing previously solvent extractedmilled rice, and in some instances, desolventizing the bran removed fromthe rice, which apparatus and method overcome the aforesaid shortcomingsof the prior art.

It is still another object of this invention to provide an improvedapparatus and method for desolventizing solvent extracted milled ricewhich preserves the integrity of the rice-kernels during the operation.1

Another object is to provide an improved extractive milling processwherein difficulties in the vapor handling and recovery systems areeliminated by feeding clean kernels of rice substantially free of loosepolish to the desolventizing operation.

Still another object is to provide an improved desolventizing procedurein an extractive milling process which minimizes chalking anddevelopment of fissures in kernels of the rice and removes residualsolvent to the desired limits.

Another object is to provide an improved extractive milling processwherein hazards due to vapor and dust explosions are minimized.

Other objects and advantages will become apparent to those skilled inthe art from the following description and the attached drawings.

An improved desolventizing procedure for the clean rice is-contemplatedwhich effects substantial savings in equipment costs, and produces adesolventized clean rice of improved appearance and free from residualsolvent. The present process also avoids problems in processing due to alarge quantity of fine bran and polish residues remaining on thefinished rice.

Briefly stated, the method of this invention contemplates passingsolvent extracted milled rice through a first chamber. A desolventizinggaseous medium comprising inert gas as the major component thereof ispassed through the first chamber to thereby vaporize solvent containedin the rice. The medium is at a temperature in the range from about to150 F. upon introduction into the first chamber. Thereafter, the mediumis withdrawn from the first chamber with the vaporized solvent containedtherein and with the medium being at a temperature within the range ofabout 95 F. to about F. A major portion of the vaporized solvent is thencondensed from the withdrawn medium, with the medium subsequently beingheated and recycled through the first chamber.

It is preferred that the medium be substantially oxygen free and thatthe inert gas portion of the medium be a combustion gas resulting from asubstantially perfect combustion of a hydrocarbon fuel. The medium willpreferably be substantially water-saturated upon withdrawal from thefirst chamber. In certain embodiments of the invention, additional inertgas is added to the medium to make up losses of gas therefrom. 1ncertain embodiments of the invention, the rice may pass to a secondchamber containing a gaseous medium comprising inert gas as the majorcomponent thereof to further desolventize the rice. in still furtherembodiments of the invention, the bran which has previously been removedfrom the rice and solvent extracted may also be desolventized with agaseous medium comprising inert gas supplied from a common source orthat used to desolventize the rice.

Briefly stated, the apparatus of this invention for desolventizingsolvent extracted milled rice includes a housing arranged for passage ofthe rice therethrough in a semi-fluidized state, with the housing havinginlet and outlet means for passing a desolventizing gaseous mediumcomprising inert gas as a major component therethroughand in intimatecontact with the rice therein to therebyvaporize solvent from the rice.The apparatusalso includes a system for generating and recycling themedium through the housing, which system comprises a gas generator forgenerating inert gas to make up the medium, a heater for heating themedium to a temperature in the range of from about 100 F. to about F.upon introduction into the housing. It also includes first conduit meansfor conducting the heated medium from the heater to the inlet of thehousing, a compressor connected to receive the medium from the outlet ofthe housing and to deliver the medium under pressure to thereby providea driving force for the medium through the housing; and a second conduitmeans arranged to receive the pressurized medium from the compressor. Italso includes condenser means connected to receive the said mediumtransmitted by the second conduit means for condensing solid vapors fromthe medium third conduit means for conducting said mediums from thecondenser to the heater, and valve means connected to be responsive tothe pressure differential between the medium in the first and secondconduit means and arrangedfor delivering additional inert gas generatedby the generator to said medium when the pressure differential exceeds apredetermined limit. Certain embodiments of the apparatus may alsoinclude means for circulating a gaseous medium through another housingthrough which the bran is passed, and in certain instances, thedesolventizing medium may be the same for both housings, as will beexplained hereinafter.

Preferably the last washing of the rice fraction is conducted with freshsolvent on a vibrating screen so that any residual particles of bran andpolish are completely removed from the rice which is again shaken on avibrating screen to free it of adhering solvent before introdu'ction ofthe rice into a desolventizer. Elimination of bran and polish particlesfrom the rice fraction prior to introducing the rice into adesolventizing step eliminates difficulties due to accumulation of thesematerials in recovery steps subsequent to desolventizing wherein thesolvent is recovered from the recirculated gas stream.

The desolventizing step preferably is conducted by passing the rice.through a housing containing warm inert gas, preferably combustiongases, for vaporizing solvent from the rice. Preferably warm inert gascontaining solvent vapor from the desolventizer passes through arecycling system in which the gas is cooled, evaporated solventcontained therein is condensed and separated from the gas, and the gasis reheated and returned to the desolventizer. Such recycle ofdesolventizer gas prevents build-up of solvent vapor in thedesolventizing gas to an explosive level, and assists in a very highrate of recovery of solvent from the used gas.

For some reason, at present unknown, a mixture of gases resulting fromsubstantially perfect combustion of a hydrocarbon material, such asnatural gas in air and containing as its principal components nitrogen,carbon dioxide and water vapor, decreases chalking of the rice duringdesolventizing and gives the rice a better appearance. It is believedthat this effect is due to theprevention'of water loss from the outerlayers of the milled kernel by. the moisture content of the inert gasmixture. 1

Reference to the drawings will further explain the invention whereinlike numerals refer to like partsandin which;

FIG. 1 is a simplified and highly schematic drawing showing thearrangement of the system for generating and recycling the gaseousmedium as taught and explained in greater detail in FIGS. 3-5.

FIG. 2 is a simplified and high schematic alternative embodiment ofanother system for generating and recyclingagaseousmedium.

FIG. 3 shows a portion of the apparatus for desolventizing the'branfraction obtained from a solvent extraction milling process.

FIG. 4 shows a portion of the system which is considered to be anextension of FIG. 3 and particularly shows one means for condensing thegaseous medium.

FIG. 5 is considered an extension of FIGS. 3 and 4 and shows inparticular one means for generating the inert gas and one means forcontacting the gaseous medium with the rice.

FIG. 6 is a generally side elevation view in schematic form showing analternate housing for contacting the rice with the gaseous medium.

FIG. 7 is a cross-sectional view taken generally along line 7-7 of FIG.6.

Referring now to the drawings, the bran cake, which has been solventextracted, is discharged directly into bran desolventizer U whichcomprisestwo or more steam-jacketed cylindrical sections 44 in each ofwhich a cutflight screw conveyor 45 receives the bran cake at the headend of each section and discharges it at the opposite end into thesucceeding cylindrical section. Steam or a hot liquid is circulated inthe jackets of the two or more cylindrical sections to heat the branmeal which quickly forms from the bran cake received into the firstsection, and causes evaporation of the solvent.

This bran meal is treated in countercurrent manner with superheatedinert gas, or a mixture of superheated inert gas and solvent vapor,which has been heated to an elevated temperature, usually within therange of 150 330 F., in recycle gas heater V (FIG. 4) and deliveredthrough duct 46 into bran'holder 47 and is circulated through the driedbran meal and escapes through duct 48 into'the lower cylindrical sectionof bran desolventizer U and continues countercurrently upward throughthe upper dryer sections and escapes through duct 49 from which it isdrawn into recycle gas blower W and is delivered by means of duct 49a torecycle gas condenser X (FIG. 4) wherein the evaporated solvent vapor iscondensed and removed as liquid solvent in the knockout drum section 50of recycle gas heater V, and is collected in solvent separator Y wherethe solvent is settled from its water content and is returned to theextraction plant by means of solvent pump Z and pipe 63.

The residual gas which comprises a mixture of inert gas and solventvapor is then reheated to a temperature of 150 330 F. and is recycledthrough duct 46 to the bran holder 47, and the cycle is repeated. Anydecrease in pressure within the recycle gas system due to gas losses orcondensation of solvent vapors by condensor X is regained by supplyinginert gas from duct 51 (FIG. 5) through differential pressure controlvalve 52 (FIG. 3) which maintains a constant differential pressurewithin the range of S to 10 feet WP. between ducts 16 and 49a, with thepressure always higher in duct 49a.

The fully desolventized, deodorized rice bran is discharged from brandesolventizer U through vapor lock 53 into bran holder 47 and is thenrecovered sequent handling of the bran are conventional and do notcomprise part of this invention.

The washed rice from the solvent extractive milling process, which stillcontains small amounts of dilute, oil-containing solvent and some polishfines, is elevated system can be supplied by readily availablecommercial generators to have an analysis substantially as follows whenburning gulf coastal natural gas:

Dry Gas Basis Carbon dioxide 12.0 per cent Unburned combustibles 0.5 percent Oxygen 0.5 per cent Nitrogen (by difference) 87.0 per centEEMPERATURE OF sa'rum'rnn oxsi F. F. 100 F. 105 F. 110 F.

Saturation humidity, (lbs.

\vatcr/lb.(1ry gas) 0.03115 0.03688 0.04312 0.06061 0.05032 Saturationmoisture, (lbs.

water/cu. it. sat. gas) 0.00214 0.00248 0.00286 0.00320 0.00877 1Pressure, 20.021 Hg.

Although the amount of moisture in the saturated inert gas is small, itis nevertheless important in the prevention of moisture loss from themilled rice during desolventizing which causes brittleness and achalkywhite appearance in the kernels. its presence also reduces thepartial pressure of the hexane and allows its removal at lowertemperatures, a function which is also common in various degrees to theother inert gas constituents. As may be seen from the preceding table,if the inert gas is delivered from generator NN at 105 F. and enters arecycle gas stream in pipe 74 from heater KK which has been heated toabove 105 F. there will be no condensation in the gas stream along itspath to desolventizer 60. However, assuming that the entering inert gasis only slightly superheated above its saturation temperature and thegas is exhausted from nozzle 68 at 95 F., there will have been amoisture loss equal to 0.05061 minus 0.03668 lbs. water/lb. dry gas fromthe entering inert gas stream to the rice and evaporated hexane.

Assuming that approximately 1.25 to 1.5 lbs. of this slightlysuperheated (above its saturation temperature) inert gas stream is usedperpound of solvent-wet rice per hour, the maximum quantity of moisturethat could be absorbed by the rice, assuming that all moisture condensedbetween the saturation temperatures of 120 and 95 F. was thus absorbedand none was absorbed in the increased volume of gases due to theevaporated hexane vaporsin the gas stream discharged from exhaust duct68, would be I 1.5 (0.05061 0.03668) 0.0290 lbs. moisture per lb. ofrice or 2.09 percent of the weight of the rice.

However, the solvent retention by the drained and vibrated rice receivedfrom desolventizing screen EE should not exceed 6 percent of the weightof the rice. Since solvent penetration into the rice kernel does notexceed a few hundredths of an inch, most of it exists as interstitialliquid solvent which together with the small amount of solvent to beremoved from the kernels is readily vaporized and removed by thesubstantially moisture saturated recycled gas. Thus, there is at mostonly inconsequential absorption of moisture from the recycled gas by therice which occurs temporarily during the volatilization of the solventwhich has only slightly penetrated its outer surface.

Rice, due to its crystalline or vitreous structure, is very sensitive totemperature changes, and particularly those that affect its normalmoisture content which ranges between 10 and 13 percent when ready formilling. Once the bran layers and germ are removed, the moisture contentwill decrease slightly. However, the milled rice is even more sensitiveto changes in temperature and in its moisture content. An advantage ofdesolventizing at a low temperature with nearly water saturatedcombustion products within a relatively narrow gas temperature range ofbetween about 100 and 150 F. (and preferably between 1 10 and 130 F.),and

' withdrawal ,of the discharged gas-hexane vapor mixture within therange of 90 to 120 F. (and preferably within the range of 90 to 110 F.),is the effective removal of the solvent without the necessity forraising the temperature of the rice.

The mean molar heat capacities of the combustion gas mixture of carbondioxide, nitrogen, trace constituents and water vapor between theentering and discharge temperature ranges above given, when used in theproportion of 1.25 to 1.50 lbs./lb. ofrice/hn, are ample to effectsubstantially complete desolventizing in section 66 of apparatus GG, butthe use of additional combustion gas in the lower deodorizing section:at temperatures ranging between and F. andin the proportion of from0.125 to 0.200 lbs/lb. rice/hr. is

' sufficient to guarantee the continuous production of an cooling, butin addition retains the sensible heat of the rice to assist indesolventizing it in section 66 in contact with the inert gas recyclestream which completes the solvent removal. The latter occurs withoutraising the temperature of the rice and further insures against checkingof the kernels.

Thus, in addition to protecting the rice from moisture losses, theintroduction of an inert gas which is only slightly superheated aboveits saturation point reduces the partial pressure of the solvent andeffects its removal at lower temperatures than is possible withsuperheated, substantially anhydrous solvent vapors which withdrawmoisture from the outer surfaces of the kernels during thevolatilization of the solvent therefrom. The latter accounts for thechalky whiteness observed in rice desolventized by the superheatedhexane recycle gas method.

The rice kernels then cool slowly in the 90 to F. atmosphere in thelower deodorizing section 75 and should be discharged from vapor lock 80into a room atmosphere which has its temperature within the range of 70to 80 F. to gradually reduce its temperature before it enters storage.

As stated above, FIG. 1 .is a simplified schematic drawing of the systemfor generating and recycling the gaseous medium as previously taught ingreater detail in reference to FIGS. 3 5. The same numerals are used todenote the same parts and the operation thereof is the same unlessstated otherwise. Hence, emphasis is here placed upon describing thesystem for handling to vibratory washer DD by means of elevator FF whereit is successively washed with pure solvent obtained from solvent pipe63 (FIG. 5). The solvent is preferably metered through rotameter 64 andis forced through' the two spray headers at the termini of solvent pipe63. The washings drain through pipe 61 to surge tank 65 which suppliespump CC. The washed rice, now substantially free of oil-containingsolvent and polish fines, but still wet with fresh rinse solvent, passesto vibratory desolventizer EE where most of the remaining surface andinterstitial solvent is shaken off and drains through pipe 61a to pipe61 and thence to surge tank 65.

The cleanly milled rice, which still contains some absorbed and surfacesolvent on the order of about 6 percent by weight or less is thendischarged at a temperature preferably in the range of about 105 toabout I l5 F. to rice desolventizer GG (FIG. 5) which, in the embodimentshown, comprises a vertical column having an upper section 66 withinternal staggered baffles, op-

positely placed recycle gas manifolds 67 and 67a, an exhaust stack 68and a hoppered bottom 69 which is equipped with a slide gate. The columnis filled and recycle gas blower l-II-I is started to establishdesolventizing gas circulation into this blower from recycle gas stack68 into exhaust duct 70 and thence into recycle gas condenser 11 whereall or any desired part of the solvent in the recycle gas may becondensed and drained to pipe 71 which delivers to solvent separator Y(FIG. 4). The remaining gas, now saturated with respect to the solventvapor and moisture, passes through duct 72 to the knockout section 73 ofrecycle gas heater KK and thence into the tubular heater section whereit is superheated to a temperature sufficient to'have evaporativeability when recycled to upper section 66 of the rice desolventizerthrough duct 74 which supplies the recycle gas manifolds 67 and 67a. Toprevent cracking of the rice, the entering gas temperature is preferablywithin the range of 100 150 F. The solvent-saturated gas leaving thedesolventizer to be recycled usually is at a temperature of 95 l20 F.

During startup, when the rice in upper section 66 is sufficientlydesolventized, the slide gate in hopper bot tom 69 is opened andcirculation into lower deodorizer section 75 of the apparatus isestablished. As desolventized rice enters section 75, additionalsolvent-wet rice enters the upper section 66. When both column sectionsare full, inert gas is admitted from pipe 76a through flow controlvalves 77 and 77a. The inert gas is forced upwards through the rice toremove the last traces of solvent, and is exhausted throughstack 78 intomain vent header 79 which collects solvent vapors from the high point ofall apparatus in which they occur. The main vent header terminates tovent condenser LL (FIG. 4) which condenses most'of the sol vent vaporsand delivers the liquid solvent to solvent Inert gas generator NNcomprises a conventional apparatus for the exact combustion of a fuel,preferably natural gas, so that the combustion produces are primarilynitrogen, carbon dioxide, water vapor and traces of oxygen, unburnedhydrocarbons and carbon monoxide which are delivered at a pressure offrom 5 to 10 psi. The main inert gas ducts 51 and 51a originate fromwater knockout pot 51b, and through several branches supply both thebran desolventizer U and the rice desolventizer and deodorizer GG with asubstantially oxygen-free inert atmosphere which will prevent explosionsof solvent vapor in all apparatus throughout the process. When drawnfrom branch inert gas pipes 76, 76a, 76b and 760 it is preferably undera moderate pressure of 2 to 3 psi. It will, therefore, flow freelythrough the deodorizer section 75 of apparatus GG and into otherapparatus and vessels in which atmospheric pressure or a slight negativepressure exists due to vent connections from them to the main ventheader which in turn connects to the vent condenser LL and from thenceto the vapor recovery system MM in which there is a final vent. Apressure of 5 to 6 psi in the main inert gas ducts 51 and 51a issufficient to deliver inert gas through differential pressure controlvalves 52 and 81 intothe return recycle gas ducts 46'and 74,respectively, to maintain a constant pressure differential between themand the recycle blowers discharge lines 49a and 70', respectively. Thus,a constant driving force is provided through both desolventizingsystems, regardless of the pressure drop through their respectiverecycle condensing and gas heating apparatus due to condensation ofsolvent vapor.

Referring to the flow diagram of the recycled gas system in FIG. 5, pipe51a and its regulating valve 81 maintain the PV relationship in therecycled gas required to provide the proper pressure differentialbetween lines 70 and 74. The blower HH withdraws through duct 68 thefull volume of the recycled desolventizing gas which enters section. 66,plus the evaporated solvent vapor from section 66 of vessel GG, andpropels this volume of gas mixture through condenser JJ, knockout 73,heater KK and pipe 74. The decrease in gas volume and the pressure dropwhich occur in condenser J], the losses of incondensibles from a ventheader connection from knockout section 73, require an inert gas makeupinto pipe 74 from pipe 51a through control valve 81 which is governed bythe unnumbered differential pressure controller. The latter is set tomaintain a selected pressure differential between pipes 70 and 74 withthe pressure always higher in pipe'70.

A further purpose of this pressure differential control system is toprovide stabilization of the system once an operational equilibrium isestablished, and, of course, to initially establish the proper pressurebalance and gas' flow rates before solvent evaporation has been fullyestablished and the operational equilibrium has been reached. To takecare of sudden pressure surges in the system due to faulty operation ofpressure control valve 81 and its differential controller, a pressurecontrol valve from the knockout section 73 apparatus KK is provided.

The inert gas delivered to the rice desolventizing system from inert gasgenerator NN, water knockout 51b and pipe 51a; and also that similarlydelivered through pipe header 51 to the bran desolventizing the gaseousmedium and reference should be made to FIGS. 3-5 for specific details,particularly concerning the handling of the rice and bran fractions inrelation to the gaseous medium. In summary then, 'inert gas generator NNsupplies a continuing source of inert gas to the desolventizing systemassociated with rice desolventizer 60 through differential pressurecontrol valve 81. The medium is withdrawn from desolventizer 06 byblower HH and transmitted to condenser JJ and thence to water knockoutsection 73 of heater KK where it is heated for recycle back todesolventizer 66.

Similarly, additional makeup inert gas is supplied from generator NNthrough differential pressure control valve 52 to line 46 whichtransmits the medium to bran desolventizer U from which it is drawn byblower W and transmitted to condenser X and thence to knockout section50 of heater V where it is heated for recycling to desolventizer U.Hence, it may be said that the desolventizing mediums for both the ricedesolventizing apparatus and the bran desolventizing apparatus areseparately condensed to remove the solvent vapors therefrom heated andrecycled.

An alternate embodiment of the system for handling the gaseous medium isshown in FIG. 2 which is somewhat simplified with respect to that shownin FIGS. 1 and 3 to 5, and which has certain advantages blower HHremoves the gaseous medium from ricedesolventizer 66 through vaporscrubber 70a, which is of conventional type and is provided with nozzlesconnected to a source of liquid solvent and arranged such that thegaseous medium is passed through afine spray which removes the bran dusttherefrom. The liquid discharge from scrubber 70a may be collected inconventional manner. The gaseous medium is then transmitted by conduit70 to heater V (which has knockout section 50 removed) where it isheated and transmitted to bran desolventizer U through ducts 46 and 48,after passage upwardly through desolventizer U. At the same time,additional inert gas is passed through bran holder 47 via line 51c whichis connected to duct 51 as shown.

it is conducted to the desolventizer unit 60 through conduit 74.

Makeup inert gas from generator NN is supplied to the system throughdifferential pressure control valves 52 and 81 in the same manner as inthe embodiment shown in FIGS. 1 and 3.t0 5.

The heavily loaded solvent vapor-inert gas stream leaves brandesolventizer U through pipe 49, and is through knockout section 73 asdescribed above.

The advantages of this modification are several:

1. The two recycled gas streams from the rice and bran desolventizersare merged into one .stream which has initially the size of the ricestream alone. Starting with inert gas from generator NN which enterspipe 74, the recycle system for desolventizer G6 is eliminated. Thevolume of desolventizing gas required in GG is relatively large becauseof the small enthalpy of the 120 F. gas which enters it. Therefore, itmay be sent directly to heater V and is recycled at a much highertemperature (240 300 F.) to the bran desolventizer U. The spent gas fromU is then condensed in condenser X where its temperature and solventcontent are both drastically reduced, from which it is returned to therice desolventizing system heater KK and thence to the ricedesolventizer G6.

2. 22,000 lbs/hr. of rice at 5 percent hexane contains 1,100 lbs/hr. ofhexane to be evaporated without heating the rice kernels to above 120 F.By concurrent evaporation, higher recycle gas temperatures can be usedwithout substantially raising the temperature of the rice kernels. 3,000lbs/hr. of wet bran will not contain over 1,200 lbs/hr. of hexane, whichis about the same quantity that is in the milled rice. The hexane in thebran may be evaporated at much higher temperatures in a very smallequipment system, especially if the modified Schneckens apparatusillustrated as desolventizer U in FIG. 3 is used. Thetemperatureincrease from 100-120 F. to 240-300 reactivates the gas as adesolventizing medium.

3. Better heat economy results. Also, besides eliminating some equipmentand considerable piping, the entire installation is more compact. A verygreat improvement in plant layout is possible.

4. The condenser water requirements of the system are reduced.

5. A better opportunity is afforded to properly trap the polish dustfrom desolventizers GG and U where it actually belongs; i.e., in thebran rather than in condensers, heaters, etc.

6. The recycle gases fromcondenser X tothe knockout section 73 of heaterKK can be supplied to desolventizer GO in cleanly washed condition dueto the heavy solvent condensation which occurs in condensor X and theelimination of solids-contaminated solvent mist in knockout section 73.

7. The desolventizing effect of a gas stream comprising a majorproportion of inert gas is high. For instance, each 1,000 cu. ft. of themixed gas stream from desolventizer G6 at 0 psig and 100 F. will contain655 cu.

.ft. of inert gas and 335 cu. ft. of hexane vapor which,

' from the rice desolventizing step, per se. This is due, of

course, to the greater solvent capacity of the hotter recycle gasstream.

The solvent used to extract the rice and bran may be any suitablecommercially available type such as hexane, heptane, trichloroethylene,ethylene dichloride,.

substantially anhydrous isopropanol, or the like, which are commonlyused insolvent extraction processes. I

Constant boiling azeotropes comprising one or more solvents with smallproportions of water are also contemplated. l-lexane is the preferredextractive solvent because of its ready availability and low cost, andits ready recovery by evaporation and stream stripping.

.. The desolventizing the clean rice may be accomplished in any ofseveral types of apparatus. However, since rice is a special caserequiring careful handling to preserve it as whole grains to thegreatest possibleextent, it is preferred that it'be desolventized in ahousing wherein the rice is placed in a semi-fluidized condition, asdoes a baffled vertical column type desolventizer similar to thatillustrated in FIG. 5, wherein the fully washed, solvent-wet, clean riceenters at the upper part of the desolventizer and is contacted by apressurized stream of inert combustion gas, or mixture of an inert gasand solvent and vapor which has been superheated to allow rapidvaporization and removal of the solvent from the rice mass as it movesdownward in a slightly expanded bed in a state of incipient fluidizationto promote rapid circulation of a desolventizing vapor within the movingbed of rice. The gases from the operation are sent in part or entirelythrough a recycled gas condenser and thence to a recycled gas heaterbefore being retumed-as superheated recycled gas'to the desolventizer.Since 90 to 95 percent of the total solids entering as brown ricearereceived and desolventized in this apparatus, it must be of highcapacity to permit fast throughput in which the rice is not subjected totemperatures exceeding 140 F.-, as temperatures above this value resultin heat checking and breakage of the rice.

The total bran and polish solids represent only about 5 to 10 percent ofthe weight of brownrice entering the process. Therefore, in a plantwhich processes 25,000 pounds of brown rice per hour, the hourly branpolish production does not necessarily exceed 2,500 pounds on the drybasis. The solvent content of the bran and polish solids entering thebyproduct solids desolventizer doesnot exceed about 50'percent by weightof these solids. While any of several type of desolventizers inclusiveof desolventizentbasters, flash desolventizer systems, and steamjacketed dryers commonly known as Schneckens apparatus, may be used indesolventizing the solids at temperatures up to 330 F., the applicantprefers to use a modified Schneckens apparatus similar to thatillustrated at U (FIG. 3) which is equipped with a holding tank at itsdischarge end to which may be introduced either saturated or superheatedgas, with or without added steam, which sweeps countercurrently throughthe solids and evaporates the solvent with the aid of indirect steamheat provided by a surrounding steam jacketor within hollow flights ofthe screw flights within the apparatus. The solvent containing inert gasis exhausted from the apparatus by a recycle gas blower and sent whollyor in part to a recycle gas condenser before being sent to the recyclegas heater from which the super-heated gas is returned to the branholding tank and the cycle is repeated.

It is to be understood that the present invention is not limited toeither a vertical cascading tower or to countercurrent flow of rice andgases in order to be carried out properly. For example, a series ofvapor-type vibrating screen conveyors equipped for either concurrent orcountercurrent flow may be used, which conveyors may be arranged end toend or in superposing relationship. Referring now to to FIGS. 6 and 7,an alternate desolventizing apparatus for the rice will be explained,which alternate embodiment may be described as a vibrating,spring-mounted drying conveyor which a may be connected to receive thegaseous medium of this invention and arranged to convey the rice in asemi-fluidized state so as to contact the gaseous medium with the rice.I

More specifically, FIG. 6 shows three such units generally designatedbythe numerals 201, 202 and 203, connected in series, and each having avibrating screen surface 204 which is arranged to advance the rice fromleft to right therealong, and a plurality of side inlets 205 which arearranged to receive the gaseous medium therethrough and to direct itupwardly through the screens 204. lnlets 205 to units 201and 202, mayfor example, be connected to conduit 74 of the'previous embodiment so asto receive the desolventizing gaseous medium thereinto.

Each of theunits 201, 202 and 203 has outlets 207 in the top thereofthrough which the gaseous medium is discharged, and in the case of units201 and 202, the outlets 207 may be connected to conduit of the previousembodiment.

The inlets 205 to unit 203 may be connected to conduit 76 of the priorembodiment thereby making unit 203 a deodorizing section, with theoutlets 207 thereof being arranged to recycle through unit 202 as shownby small blowers or the like.

The sections or units 201, 202 and 203 may be arranged in horizontalsequence as shown above, or in vertical stacked alignment. In concurrentflow, the gaseous medium enters the inlets 205 as described and riceenters through vapor lock A. The desolventizing medium leaves at theupper outlets 207, as described above, and the partially desolventizedrice then travels to unit 202 where it is contacted with additionalgaseous medium, which may be made up from recycled gas and fresh inertgas from unit 203. The desolventized, deodorized rice leaves unit 203through a vapor lockB.

When units 201, 202 and 203 are stacked vertically,

the sequence is the same. Intermediate vapor locks between the sectionsare not required when the first unit, i.e., 201 is fed concurrently. Thesame applies to unit 202. There may also be small countercurrent recycleblowers between subsections of each unit 201, 202 and 203.

' It is to be understood that other types of desolventizingapparatuscould be used, including non-vibrating conveyors of the fluidized bedtyp'e, rotating cylinders fitted with lifters, or moving belts in vaporlocked horizontal or vertical enclosures'or the like.

Further modifications may be made in the invention as particularlydescribed without departing from the scope thereof. Accordingly, theforegoing description is to be construed as illustratively only and notas a limitation upon the invention as defined in the following claims.

What is claimed is:

1. ln apparatus for desolventizing solvent extracted milled rice, thecombination comprising:

.a housing arranged for passage of said rice therethrough in asemi-fluidized state, said housing having inlet and outlet means forpassing a desolventizing gaseous medium comprising inert gas as themajor component therethrough and in intimate contact with said ricetherein to thereby vaporize solvent from said rice; and a system forgenerating and recycling said medium through said housing, said systemcomprising;

a gas generator for generating said inert gas;

a heater for heating said medium to a temperature in-the range of fromabout 100 F. to about 150 F. 'upon introduction into said housing;

first conduit means for conducting said medium from said heater to saidinlet means of said housa compressor connected to receive said mediumfrom said outlet means of said housing, and to deliver said medium underpressure to thereby provide a driving force for said medium through saidhousing;

second conduit means arranged to receive said pressurized medium fromsaid compressor;

condenser meansconnected to receive said medium transmitted by saidsecond conduit means for condensing solvent vapors from said medium;

third conduit means for conducting said medium from said condenser tosaid heater; and

valve means connected to be responsive to the pressure differentialbetween said medium in said first and second conduit means and arrangedfor delivering additional inert gas generated by said generator to saidmedium when said pressure differential exceeds a predetermined limit.

2. The invention as claimed in claim 1 including:

a second housing arranged for passage therethrough of solvent extractedbran previously removed from said rice, said housing having an inlet andoutlet;

means for heating and passing a desolventizing gaseous medium comprisinginert gas as the major component through said second housing in intimatecontact with said bran therein at a desolventizing temperature tothereby vaporize solvent from said bran; and

second valve means connected for supplying inert gas from said generatorto said medium circulated through said second housing.

3. The invention as claimed in claim 2 including:

a second condenser connected to receive the medium passed through saidsecond housing, whereby said medium used to d'esolventize said bran isseparated from that medium used to desolventize said rice and isseparately recycled.

4. The invention as claimed in claim 2 wherein: sald second conduitmeans lS connected to said means for heating and passing a mediumthrough said second housing; and the outlet means of said second housingis connected to deliver said medium to said condenser; whereby saidmedium is successively recycled through said first and second housings.

1. In apparatus for desolventizing solvent extracted milled rice, thecombination comprising: a housing arranged for passage of said ricetherethrough in a semi-fluidized state, said housing having inlet andoutlet means for passing a desolventizing gaseous medium comprisinginert gas as the major component therethrough and in intimate contactwith said rice therein to thereby vaporize solvent from said rice; and asystem for generating and recycling said medium through said housing,said system comprising; a gas generator for generating said inert gas; aheater for heating said medium to a temperature in the range of fromabout 100* F. to about 150* F. upon introduction into said hOusing;first conduit means for conducting said medium from said heater to saidinlet means of said housing; a compressor connected to receive saidmedium from said outlet means of said housing, and to deliver saidmedium under pressure to thereby provide a driving force for said mediumthrough said housing; second conduit means arranged to receive saidpressurized medium from said compressor; condenser means connected toreceive said medium transmitted by said second conduit means forcondensing solvent vapors from said medium; third conduit means forconducting said medium from said condenser to said heater; and valvemeans connected to be responsive to the pressure differential betweensaid medium in said first and second conduit means and arranged fordelivering additional inert gas generated by said generator to saidmedium when said pressure differential exceeds a predetermined limit. 1.In apparatus for desolventizing solvent extracted milled rice, thecombination comprising: a housing arranged for passage of said ricetherethrough in a semi-fluidized state, said housing having inlet andoutlet means for passing a desolventizing gaseous medium comprisinginert gas as the major component therethrough and in intimate contactwith said rice therein to thereby vaporize solvent from said rice; and asystem for generating and recycling said medium through said housing,said system comprising; a gas generator for generating said inert gas; aheater for heating said medium to a temperature in the range of fromabout 100* F. to about 150* F. upon introduction into said hOusing;first conduit means for conducting said medium from said heater to saidinlet means of said housing; a compressor connected to receive saidmedium from said outlet means of said housing, and to deliver saidmedium under pressure to thereby provide a driving force for said mediumthrough said housing; second conduit means arranged to receive saidpressurized medium from said compressor; condenser means connected toreceive said medium transmitted by said second conduit means forcondensing solvent vapors from said medium; third conduit means forconducting said medium from said condenser to said heater; and valvemeans connected to be responsive to the pressure differential betweensaid medium in said first and second conduit means and arranged fordelivering additional inert gas generated by said generator to saidmedium when said pressure differential exceeds a predetermined limit. 2.The invention as claimed in claim 1 including: a second housing arrangedfor passage therethrough of solvent extracted bran previously removedfrom said rice, said housing having an inlet and outlet; means forheating and passing a desolventizing gaseous medium comprising inert gasas the major component through said second housing in intimate contactwith said bran therein at a desolventizing temperature to therebyvaporize solvent from said bran; and second valve means connected forsupplying inert gas from said generator to said medium circulatedthrough said second housing.
 3. The invention as claimed in claim 2including: a second condenser connected to receive the medium passedthrough said second housing, whereby said medium used to desolventizesaid bran is separated from that medium used to desolventize said riceand is separately recycled.